1. Technical Field
This invention relates to a water purification system using intense ultraviolet irradiation to break down chemical bonds in toxic compounds and to de-activate pathogens. The method can also be applied to any mass transport, including the purification of air. These systems can be applied to purify fluids containing naturally occurring toxins or those resulting from biological and chemical agents used in warfare.
2. Background Art
The first application of an ultraviolet (UV) low-pressure mercury vapor discharge lamp to disinfect water was in Marseilles, France in 1901. However, it was not until 1955 that UV disinfection became widely applied in Europe for potable water. In that year UV disinfection equipment was installed in Switzerland, Austria and Norway. Following the discovery of the formation of halogenated hydrocarbons during chlorination, UV disinfection since became popular in most European countries.
U.S. Pat. No. 1,196,481, issued Aug. 29, 1916 described the use of a mercury vapor lamp to generate sufficient ultraviolet light (mostly 254-nm wavelength) to purify water. Further refinements have been made over the years, such as in Ellner U.S. Pat. No. 3,182,193 issued May 4, 1965, Maarschalkerweerd U.S. Pat. No. 4,482,809 issued Nov. 13, 1984, Moyher U.S. Pat. No. 5,069,782 issued Dec. 3, 1991, Tiede U.S. Pat. No. 5,393,419 issued Feb. 28, 1995, and Anderson U.S. Pat. No. 6,099,799 issued Aug. 8, 2000. Much of the latter art referenced above improved upon aspects related to commercial viability, such as improving UV dosage uniformity through the use of baffles, UV-transparent coils, and controlled turbulence; increasing UV intensity for higher flow rates by increasing the number of lamps in a given volume; and improving maintenance through the use of Teflon coatings, wiper mechanisms, and adding turbulence.
Central to the present invention is the maximization of UV contact-time with the water, as opposed to being absorbed by the walls of the container.
It's well known to those familiar with the art that many of the UV water disinfecting systems utilize stainless steel water jackets, owing at least in part to its history of use in fluid applications requiring sanitary operation. It's viability as an efficient UV reflector, however, is marginal, with data showing less than 40% reflectance at normal for the germicidal wavelengths around 250 nm (J. Zwinkels, et al, pgs 7933–7944, Applied Optics, Vol. 33, No. 34, 1 Dec. 1994).
Prior art portable UV disinfection systems are described, for example, in U.S. Pat. No. 5,900,212 as well as PCT publication WO 01/28933. The '212 utilizes a portable UV source placed in a container whose walls are of unknown reflectance. In the PCT publication, a UV-transparent window allows sunlight through, only to strike the container walls, again of unkown reflectance.
Improvements in reflectance is discussed in Stanley Jr, U.S. Pat. No. 5,413,768, whereby water is guided through a high tensile strength container having an interior surface that is highly reflective to UV (such as aluminum). The container is further lined with an FEP layer up to 10 mm thick and anchored to the container, for example via ridges formed by routing the interior of the container. While FEP is generally thought to be transmissive in the UV, it will be shown that thick layers are in fact absorptive.
It will be shown that in applications where the water being irradiated is “polished”, the walls of prior art systems absorb a high proportion of the incident UV.
It will also be shown that in the present invention, there is substantial efficiency benefits in using total internal reflection as the primary means of maximizing contact time between UV and the fluid.